In mobile telecommunication networks, a serving mobile switching center (“S-MSC”) and an originating mobile switching center (“O-MSC”) serve to connect a call from a communication device to a mobile device that is supported by the serving mobile switching center. For example, the mobile device comprises a roaming mobile device. The originating mobile switching center supports call delivery to the serving mobile switching center and the serving mobile switching center supports an air interface connection with the mobile device.
To initiate the call to the mobile device, the communication device initiates a call setup message to the originating mobile switching center. In one example, the mobile telecommunication network comprises an American National Standards Institute (“ANSI-41”) network. The originating mobile switching center sends a location request invoke operation/message (“LOCREQ”) to a home location register (“HLR”) to determine the location of the mobile device. The home location register checks a record associated with the mobile device and in one example determines that the mobile device is registered at the serving mobile switching center. Therefore, the home location register sends a routing request invoke message/operation (“ROUTREQ”) to the serving mobile switching center. In another example, the mobile telecommunication network comprises a Global System for Mobile Communications (“GSM”) network and employs GSM mobile application part (“MAP”) messages for call delivery. For example, the GSM network employs a send routing information (“SRI”) message and a provide roaming number (“PRN”) message to initiate delivery of the call to the mobile device.
Upon receipt of the routing request invoke message, the serving mobile switching center allocates a temporary roaming number for the call from a pool of available temporary roaming numbers. In one example, the mobile telecommunication network comprises an ANSI-41 network and the temporary roaming number comprises a temporary local directory number (“TLDN”). In another example, the mobile telecommunication network comprises a GSM network and the temporary roaming number comprises a mobile subscriber roaming number (“MSRN”). The serving mobile switching center sends the temporary roaming number to the home location register in a routing request return result operation/message (“routreq”). The home location register sends the temporary roaming number to the originating mobile switching center in a location request return result operation/message (“locreq”). The GSM network employs a provide roaming number acknowledgement message and a send routing information acknowledgement message to return the temporary roaming number.
The serving mobile switching center associates the temporary roaming number with the mobile device and awaits an incoming call that indicates the temporary roaming number as a called party number. Upon receipt of the temporary roaming number, the originating mobile switching center sends the call to the serving mobile switching center over a trunk. In one example, the trunk signaling comprises Integrated Services Digital Network User Part (“ISUP”) signaling. Thus, the originating mobile switching center sets the called party number of an initial address message (“IAM”) to the temporary roaming number. The originating mobile switching center sends the initial address message to the serving mobile switching center to pass the call to the serving mobile switching center.
Upon receipt of the initial address message, the serving mobile switching center searches for the mobile device that is associated with the temporary roaming number in a list of active temporary roaming numbers. Upon finding the mobile device, the serving mobile switching center proceeds with call termination processing, which may include paging the mobile device to indicate the incoming call. Upon connection of the call with the mobile device, the serving mobile switching center returns the temporary roaming number to the pool of available temporary roaming numbers.
The serving mobile switching center must keep a pool of available temporary roaming numbers that is large enough to handle incoming calls to roaming mobile devices. For example, the pool of available temporary roaming numbers may comprise one thousand telephone numbers reserved for incoming call delivery to the roaming mobile devices. As one shortcoming, the pool of available temporary roaming numbers are unavailable for other uses. For example, the pool of available temporary roaming numbers may contribute to a shortage of telephone numbers. As another shortcoming, if the pool of available temporary roaming numbers are all assigned at a given time, then the serving mobile switching center is unable to handle new incoming calls to the roaming mobile devices. As yet another shortcoming, the serving mobile switching center must have storage space available to keep a record of the assignment of temporary roaming numbers.
Thus, a need exists for a delivery system for incoming calls to roaming mobile devices that promotes a reduction in a number of reserved temporary roaming numbers.